1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a record medium, which includes a record medium determining device to irradiate a laser light to the record medium, to detect a reflected light thereof, and to determine the kind of the record medium from the distribution state of the reflected light.
2. Description of the Related Art
In order to perform excellent image formation in an image forming apparatus such as a copier or a printer, it is necessary to adjust a printing method according to the kind of a record medium, such as a sheet, on which an image is formed. For example, unless the printing method is adjusted in a case where printing is performed on a plain paper and a case where printing is performed on an OHP sheet, an excellent image can not be obtained.
In an early model, although an operator manually selects the kind of a record medium, since there is a case where an erroneous selection is made, the development of a device to detect the kind of the record medium has been advanced.
In the related art, there is proposed a device in which a light is irradiated to a record medium, and a reflected light thereof and a transmitted light thereof are detected (for example, JP-A-2006-58261).
This is such that with respect to the light from a first light emitting source, the received light amount of the transmitted light is detected by a first light receiving element disposed at a position opposite to the first light emitting source across the record medium, and with respect to the light from a second light emitting source, the received light amount of the reflected light is detected by a light receiving element disposed on the same side as the second light emitting source with respect to the record medium, and these received light amounts are compared with threshold values to determine the kind of the record medium.
However, in this technique, there is a problem that although it is possible to determine record media, like an OHP sheet and a plain paper, in which the received light amounts of the transmitted lights and the received light amounts of the reflected lights are much different from each other, when the received light amounts of the transmitted lights and the received light amounts of the reflected lights become approximate to each other like a plain paper and a recycle plain paper, the accuracy of determination is reduced.
In order to solve this problem, there is proposed a device in which a light is irradiated to a record medium, and a reflected light thereof is detected by an area sensor (for example, JP-A-2003-205654).
This is such that the reflected light is received by a two-dimensional surface, an average value, a maximum value and a minimum value are calculated from the amount of received light, and they are compared with threshold values to determine the kind of the record medium.
However, as described later, in this technique, the range of the reflected light which can be received by the area sensor is limited, and there is a problem that the kind of the record medium which can be determined from the pattern of the detectable reflected light is limited.